1. Field of the Invention
The present invention relates to an improved gas supply system equipped with a pressure-type flow rate control unit for use in semiconductor manufacturing facilities and chemical manufacturing plants. More particularly, the present invention relates to a gas supply system reduced in size and improved in flow rate control and other performances.
2. Description of the Prior Art
The mass flow rate controller has been widely used for gas flow rate control in the gas supply system in semiconductor manufacturing facilities.
But the mass flow rate controller has presented a number of problems in practice including high manufacturing costs, slow response, product-to-product control precision non-uniformity, and low control stability.
Similarly, the metal diaphragm valve of the air-driven type has found wide acceptance as a valve to control the supply of gas from the gas supply source to gas-using processes. But this valve is slow to open and close, which lowers reliability of the quality of the finished products, i.e., semiconductors, and fails to raise the production efficiency of semiconductors and other products.
Earlier, the applicants of the present invention developed a gas supply system using a pressure-type flow rate controller and a high-speed solenoid actuating type metal diaphragm valve which could solve all the problems with the prior art. The new supply system developed was disclosed in unexamined Japanese patent applications laid open under Nos. H08-338546 and H10-55218.
FIG. 11 shows a block diagram of a gas supply system equipped with the prior art pressure-type flow rate control unit. FIG. 12 is a vertical, sectional view showing a control valve and an orifice-accompanying valve installed together which constitutes the core of the gas supply system.
In FIGS. 11 and 12, the numeral 1 indicates a pressure-type flow rate control unit, 2 a control valve, 3 a pressure detector, 4 a temperature detector, 5 an orifice, 6 a calculation control unit, 6a an temperature correction circuit, 6b a flow rate calculation circuit, 6c a comparison circuit, 6d an amplifier circuit, 7a, 7b amplifiers, 8a, 8b A/D converters, 9 an orifice-accompanying valve, 9a a valve block and 12 a valve block. The reference letters Qs denote flow-rate specifying signal, Qc flow-rate calculation signal and Qy control signal. The operating principle of that pressure-type flow rate control system is this: The fluid pressure between the orifice 5 and the control valve 2 is measured by the pressure detector 3 with the pressure P1 on the upstream side of the orifice 5 held about twice or more higher than the downstream pressure P2. On the basis of this detected pressure P1, the flow rate Qc is calculated with an equation Qc=KP1 (K: constant) in the calculation control unit 6. The difference between the flow-rate specifying signal Qs and the calculated flow rate Qc is input in the drive 10 for the valve 2 as control signal Qy to regulate the opening of the control valve 2 for adjusting the pressure P1 upstream of the orifice 5 so that the flow rate on the downstream side of the orifice 5 is automatically regulated to the specified flow rate Qs.
The control valve 2 and the orifice-accompanying valve 9 are formed separately as shown in FIG. 12. The two valves 2, 9, which are connected to each other by means of a nipple 12a and a connecting bolt 13a, form the core of the gas supply system.
The orifice-accompanying valve 9 as used is an air-actuating type diaphragm valve or solenoid-actuating type metal diaphragm valve.
Also, in FIGS. 11 and 12, the numeral 11a indicates the gas outlet side, 11b the gas inlet side, 12a, 12b nipples, and 13b, 13a connecting bolts.
The gas supply system equipped with the known pressure-type flow rate control unit shown in FIGS. 11 and 12 was much lower in manufacturing costs and more excellent in response characteristics than the system using the prior art mass flow rate controller. Also unsurpassed by the prior art mass flow rate controller in control precision, the pressure-type flow rate control unit has an excellent usefulness in practice.
Yet, the above-mentioned gas supply system equipped with the pressure-type flow rate control unit still has some problems to solve. That which requires urgent attention is the necessity:
to further reduce size; PA1 to so design the components that the surfaces coming in contact with gas are easy to treat, thus raising the stability and reliability of the components; PA1 to improve the transient flow rate characteristics to prevent the so-called overshoot (transient flow-in) and keep the mixture gas from fluctuating in composition ratio, thus raising the uniformity of quality of finished products or semiconductors; and PA1 to speed up the switchover of gases to supply, thus improving the production efficiency.